The fiercest fighting of the Salvadoran civil war is underway in northern Morazan Province, according to government military spokesmen and rebel radio broadcasts.

The combat appears to stem from a growing guerrilla initiative as the insurgents step up their activities throughout the country, especially in the troubled eastern provinces, striking at power lines and plunging the provincial capitals of both Usulutan and San Miguel into darkness, dynamiting bridges and blowing up buses.

But the action in Morazan, where the guerrillas of the Revolutionary Peoples' Army faction have long dominated the rugged mountains, appears to be on a scale unmatched in rural combat here.

In one engagement alone, between the villages of Torola and San Fernando, the rebels say they have surrounded a detachment of more than 135 government troops, killing as many as 50 of the soldiers and taking several others prisoner.

One Salvadoran Army commander who visited the provincial capital on Friday described the situation as "confused," and Army spokesman Col. Marco Aurelio Gonzalez said today that he could not release the number of soldiers who have "disappeared"--missing in action or taken prisoner--but that eight were confirmed killed in the fighting and another 28 were wounded.

Asked if the battle was the toughest of the war, Gonzalez answered with a flat, "yes."

The battle for Morazan began when guerrillas routed the small government garrison in Perquin and took the village on June 5.

With the rainy season now fully under way and clouds hugging the broken terrain, helicopters have not been able to bring in government reinforcements, according to Gonzalez, and the only major road leading to the towns is cut.

Troops now estimated by some unofficial sources to number as many as 2,000 have had to make their way toward the fighting on foot and "under fire," according to Gonzalez.